Re: [PATCH v5 1/3] drm/xe/sysctrl: Add sysctrl debugfs infrastructure and loopback test interface

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Thu, Sep 10, 2026 at 10:56:20AM -0700, Anoop, Vijay wrote:
> From: Anoop Vijay <anoop.c.vijay@intel.com>
> 
> Add debugfs support for exercising System Controller mailbox
> interface from userspace. This adds the "sc/" debugfs root
> directory and a "loopback" entry that sends an arbitrary byte
> payload to the Core group's inverted-loopback command (group=0xFF,
> cmd=0x03) and reports the response:
> 
>   echo "0x11 0x22 0x33 0x44" > /sys/kernel/debug/dri/0/sc/loopback
>   cat /sys/kernel/debug/dri/0/sc/loopback
> 
> Signed-off-by: Anoop Vijay <anoop.c.vijay@intel.com>
> ---
> v5:
> - Add per-entry locking for debugfs accesses
> - Drop unused xe_device.h include
> 
> v4 (Rodrigo):
> - Squashed debugfs infrastructure and loopback support into a single commit
> ---
>  drivers/gpu/drm/xe/Makefile                   |   1 +
>  drivers/gpu/drm/xe/xe_debugfs.c               |   5 +
>  drivers/gpu/drm/xe/xe_sysctrl_debugfs.c       | 167 ++++++++++++++++++
>  drivers/gpu/drm/xe/xe_sysctrl_debugfs.h       |  14 ++
>  drivers/gpu/drm/xe/xe_sysctrl_mailbox_types.h |   2 +
>  drivers/gpu/drm/xe/xe_sysctrl_types.h         |  38 ++++
>  6 files changed, 227 insertions(+)
>  create mode 100644 drivers/gpu/drm/xe/xe_sysctrl_debugfs.c
>  create mode 100644 drivers/gpu/drm/xe/xe_sysctrl_debugfs.h
> 
> diff --git a/drivers/gpu/drm/xe/Makefile b/drivers/gpu/drm/xe/Makefile
> index 67b8b5477639..3484e9a523d1 100644
> --- a/drivers/gpu/drm/xe/Makefile
> +++ b/drivers/gpu/drm/xe/Makefile
> @@ -128,6 +128,7 @@ xe-y += xe_bb.o \
>  	xe_survivability_mode.o \
>  	xe_sync.o \
>  	xe_sysctrl.o \
> +	xe_sysctrl_debugfs.o \
>  	xe_sysctrl_event.o \
>  	xe_sysctrl_mailbox.o \
>  	xe_tile.o \
> diff --git a/drivers/gpu/drm/xe/xe_debugfs.c b/drivers/gpu/drm/xe/xe_debugfs.c
> index 80f62634fae5..7c6af4f7a3fa 100644
> --- a/drivers/gpu/drm/xe/xe_debugfs.c
> +++ b/drivers/gpu/drm/xe/xe_debugfs.c
> @@ -31,6 +31,8 @@
>  #include "xe_sriov_pf_debugfs.h"
>  #include "xe_sriov_vf.h"
>  #include "xe_step.h"
> +#include "xe_sysctrl.h"
> +#include "xe_sysctrl_debugfs.h"
>  #include "xe_tile_debugfs.h"
>  #include "xe_ttm_vram_mgr.h"
>  #include "xe_vsec.h"
> @@ -836,6 +838,9 @@ void xe_debugfs_register(struct xe_device *xe)
>  
>  	xe_fault_inject_debugfs_register(xe, root);
>  
> +	if (xe->info.has_sysctrl)
> +		xe_sysctrl_debugfs_register(&xe->sc, root);
> +
>  	if (IS_SRIOV_PF(xe))
>  		xe_sriov_pf_debugfs_register(xe, root);
>  	else if (IS_SRIOV_VF(xe))
> diff --git a/drivers/gpu/drm/xe/xe_sysctrl_debugfs.c b/drivers/gpu/drm/xe/xe_sysctrl_debugfs.c
> new file mode 100644
> index 000000000000..c0454c4c0ae0
> --- /dev/null
> +++ b/drivers/gpu/drm/xe/xe_sysctrl_debugfs.c
> @@ -0,0 +1,167 @@
> +// SPDX-License-Identifier: MIT
> +/*
> + * Copyright © 2026 Intel Corporation
> + */
> +
> +#include <linux/cleanup.h>
> +#include <linux/debugfs.h>
> +#include <linux/err.h>
> +#include <linux/kstrtox.h>
> +#include <linux/seq_file.h>
> +#include <linux/slab.h>
> +#include <linux/string.h>
> +#include <linux/uaccess.h>
> +
> +#include "xe_pm.h"
> +#include "xe_printk.h"
> +#include "xe_sysctrl.h"
> +#include "xe_sysctrl_debugfs.h"
> +#include "xe_sysctrl_mailbox.h"
> +#include "xe_sysctrl_mailbox_types.h"
> +#include "xe_sysctrl_types.h"
> +
> +static ssize_t xe_sysctrl_loopback_write(struct file *file, const char __user *ubuf,
> +					 size_t len, loff_t *offp)
> +{
> +	char *kbuf __free(kfree) = NULL;
> +	u8 *input __free(kfree) = NULL;
> +	struct seq_file *m = file->private_data;
> +	struct xe_sysctrl_debugfs_entry *entry = m->private;
> +	struct xe_device *xe = sc_to_xe(entry->sc);
> +	struct xe_sysctrl_mailbox_command cmd = {};
> +	char *token, *tmp;
> +	unsigned long val;
> +	size_t input_len = 0;
> +	size_t max_input;
> +	size_t out_len = 0;
> +	int status;
> +

probably worth adding here:

        if (*pos)
                 return -ESPIPE;

> +	if (len == 0 || len >= PAGE_SIZE)
> +		return -EINVAL;
> +
> +	kbuf = kmalloc(len + 1, GFP_KERNEL);
> +	if (!kbuf)
> +		return -ENOMEM;
> +
> +	max_input = min_t(size_t, len, XE_SYSCTRL_MB_MAX_MESSAGE_SIZE);

don't you need to consider the header as well here?
Or it might pass here and fail in sysctrl_prepare_command()

no?!

> +	input = kmalloc(max_input, GFP_KERNEL);
> +	if (!input)
> +		return -ENOMEM;
> +
> +	if (copy_from_user(kbuf, ubuf, len))
> +		return -EFAULT;
> +	kbuf[len] = '\0';
> +
> +	tmp = kbuf;
> +	while ((token = strsep(&tmp, " \t\n")) != NULL) {
> +		if (*token == '\0')
> +			continue;
> +
> +		if (input_len >= max_input) {
> +			xe_err(xe, "sysctrl: loopback payload too large (max %d bytes)\n",
> +			       XE_SYSCTRL_MB_MAX_MESSAGE_SIZE);
> +			return -EINVAL;
> +		}
> +
> +		if (kstrtoul(token, 0, &val) || val > 0xFF) {
> +			xe_err(xe, "sysctrl: invalid loopback token '%s'\n", token);
> +			return -EINVAL;
> +		}
> +
> +		input[input_len++] = (u8)val;
> +	}
> +
> +	if (input_len == 0) {
> +		xe_err(xe, "sysctrl: no loopback payload given\n");
> +		return -EINVAL;
> +	}
> +
> +	xe_sysctrl_create_command(&cmd, entry->group, entry->command,
> +				  input, input_len, entry->response_buf, input_len);
> +
> +	scoped_guard(mutex, &entry->lock) {
> +		guard(xe_pm_runtime)(xe);
> +		entry->status = xe_sysctrl_send_command(entry->sc, &cmd, &out_len);
> +		entry->response_len = entry->status ? 0 : out_len;
> +		status = entry->status;
> +	}
> +
> +	return status ? status : len;
> +}
> +
> +static int xe_sysctrl_loopback_show(struct seq_file *m, void *data)
> +{
> +	struct xe_sysctrl_debugfs_entry *entry = m->private;
> +	size_t i;
> +
> +	guard(mutex)(&entry->lock);
> +
> +	seq_printf(m, "Command: group=0x%02x cmd=0x%02x\n", entry->group, entry->command);
> +	seq_printf(m, "Status: %d (%s)\n", entry->status, entry->status ? "FAILED" : "SUCCESS");
> +	seq_printf(m, "Response: %zu bytes\n", entry->response_len);
> +
> +	if (entry->response_len) {
> +		seq_puts(m, "Response data:\n");
> +		for (i = 0; i < entry->response_len; i++) {
> +			if (i && (i % 16) == 0)
> +				seq_putc(m, '\n');
> +			seq_printf(m, "%02x ", entry->response_buf[i]);
> +		}
> +		seq_putc(m, '\n');
> +	}
> +
> +	return 0;
> +}
> +
> +static int xe_sysctrl_loopback_open(struct inode *inode, struct file *file)
> +{
> +	return single_open(file, xe_sysctrl_loopback_show, inode->i_private);
> +}
> +
> +static const struct file_operations xe_sysctrl_loopback_fops = {
> +	.owner = THIS_MODULE,
> +	.open = xe_sysctrl_loopback_open,
> +	.read = seq_read,
> +	.write = xe_sysctrl_loopback_write,
> +	.llseek = seq_lseek,
> +	.release = single_release,
> +};
> +
> +static void xe_sysctrl_register_entry(struct dentry *root, struct xe_sysctrl_debugfs_entry *entry,
> +				      struct xe_sysctrl *sc, const char *name,
> +				      u8 group, u8 command,
> +				      const struct file_operations *fops)
> +{
> +	struct xe_device *xe = sc_to_xe(sc);
> +
> +	if (devm_mutex_init(xe->drm.dev, &entry->lock))
> +		return;

should we propagate the error up or at least warn here?

> +
> +	entry->sc = sc;
> +	entry->group = group;
> +	entry->command = command;
> +	entry->response_len = 0;
> +	entry->status = 0;
> +
> +	debugfs_create_file(name, 0644, root, entry, fops);
> +}
> +
> +/**
> + * xe_sysctrl_debugfs_register - Register debugfs entries for System Controller
> + * @sc: xe_sysctrl instance
> + * @parent: parent debugfs directory
> + */
> +void xe_sysctrl_debugfs_register(struct xe_sysctrl *sc, struct dentry *parent)
> +{
> +	struct dentry *root;
> +
> +	root = debugfs_create_dir("sc", parent);
> +	if (IS_ERR(root))
> +		return;
> +
> +	sc->debugfs.root = root;
> +
> +	xe_sysctrl_register_entry(root, &sc->debugfs.loopback, sc, "loopback",
> +				  XE_SYSCTRL_GROUP_CORE, XE_SYSCTRL_CMD_LOOPBACK,
> +				  &xe_sysctrl_loopback_fops);
> +}
> diff --git a/drivers/gpu/drm/xe/xe_sysctrl_debugfs.h b/drivers/gpu/drm/xe/xe_sysctrl_debugfs.h
> new file mode 100644
> index 000000000000..d1414ac3562e
> --- /dev/null
> +++ b/drivers/gpu/drm/xe/xe_sysctrl_debugfs.h
> @@ -0,0 +1,14 @@
> +/* SPDX-License-Identifier: MIT */
> +/*
> + * Copyright © 2026 Intel Corporation
> + */
> +
> +#ifndef _XE_SYSCTRL_DEBUGFS_H_
> +#define _XE_SYSCTRL_DEBUGFS_H_
> +
> +struct dentry;
> +struct xe_sysctrl;
> +
> +void xe_sysctrl_debugfs_register(struct xe_sysctrl *sc, struct dentry *parent);
> +
> +#endif
> diff --git a/drivers/gpu/drm/xe/xe_sysctrl_mailbox_types.h b/drivers/gpu/drm/xe/xe_sysctrl_mailbox_types.h
> index c236e5377f30..501a4a4c16ff 100644
> --- a/drivers/gpu/drm/xe/xe_sysctrl_mailbox_types.h
> +++ b/drivers/gpu/drm/xe/xe_sysctrl_mailbox_types.h
> @@ -47,9 +47,11 @@ enum xe_sysctrl_gfsp_cmd {
>  /**
>   * enum xe_sysctrl_core_cmd - Commands supported by Core group
>   *
> + * @XE_SYSCTRL_CMD_LOOPBACK: Loopback test command
>   * @XE_SYSCTRL_CMD_GET_APP_STATUS_BY_ID: Retrieve application status by ID
>   */
>  enum xe_sysctrl_core_cmd {
> +	XE_SYSCTRL_CMD_LOOPBACK				= 0x03,
>  	XE_SYSCTRL_CMD_GET_APP_STATUS_BY_ID		= 0x05,
>  };
>  
> diff --git a/drivers/gpu/drm/xe/xe_sysctrl_types.h b/drivers/gpu/drm/xe/xe_sysctrl_types.h
> index 98c2f473f7c6..9ad3c40de97a 100644
> --- a/drivers/gpu/drm/xe/xe_sysctrl_types.h
> +++ b/drivers/gpu/drm/xe/xe_sysctrl_types.h
> @@ -10,7 +10,36 @@
>  #include <linux/types.h>
>  #include <linux/workqueue_types.h>
>  
> +#include "xe_sysctrl_mailbox_types.h"
> +
>  struct xe_mmio;
> +struct dentry;
> +
> +/**
> + * struct xe_sysctrl_debugfs_entry - Debugfs entry for a raw mailbox test command
> + */
> +struct xe_sysctrl_debugfs_entry {
> +	/** @sc: Back pointer to parent sysctrl instance */
> +	struct xe_sysctrl *sc;
> +
> +	/** @group: Command group ID */
> +	u8 group;
> +
> +	/** @command: Command ID within group */
> +	u8 command;
> +
> +	/** @lock: Protects @status, @response_len and @response_buf below */
> +	struct mutex lock;
> +
> +	/** @response_buf: Response data buffer, sized to the maximum mailbox message */
> +	u8 response_buf[XE_SYSCTRL_MB_MAX_MESSAGE_SIZE];
> +
> +	/** @response_len: Actual response length from firmware */
> +	size_t response_len;
> +
> +	/** @status: Last command result */
> +	int status;
> +};
>  
>  /**
>   * struct xe_sysctrl - System Controller driver context
> @@ -31,6 +60,15 @@ struct xe_sysctrl {
>  
>  	/** @event_lock: Mutex protecting pending events */
>  	struct mutex event_lock;
> +
> +	/** @debugfs: Debugfs entries */
> +	struct {
> +		/** @debugfs.root: Root debugfs directory */
> +		struct dentry *root;
> +
> +		/** @debugfs.loopback: Loopback test entry */
> +		struct xe_sysctrl_debugfs_entry loopback;
> +	} debugfs;
>  };
>  
>  #endif
> -- 
> 2.43.0
>